In the electric meter box art it is becoming increasingly necessary to provide positive means for locking the cover of the meter box closed, to prevent unauthorized persons from gaining access to the terminals inside the box. Locking is often accomplished by the use of a so-called barrel lock or plunger lock, such as is shown in my U.S. Pat. No. 3,186,196 issued June 1, 1965.
This lock comprises a housing and a pair of balls which are moved outwardly into the locking position by an internal axially movable plunger. The plunger is spring biased to the locking position, and is moved to the unlocking position by the insertion of an expandable tool into the end of a hollow stem of the plunger. The tool frictionally grips the internal walls of the stem so that tension can be applied to the plunger to pull it, against the force of the spring, to the unlocking position.
However, it has been found that it is possible to jam an article, such as a wire with a suitably bent end, into the stem cavity and with sufficient perseverance to obtain sufficient frictional engagement with the internal stem wall to pull the plunger to the unlocking position.
Also, tools for opening such locks are often lost or stolen, and find their way into the hands of unauthorized persons.